THE FACIAL. 547 



operation on dogs and rabbits, the animals were still capable of wink- 

 ing with both eyes ; only the action of the two nerves was no longer 

 simultaneous, and the closure of each eye was performed at irregular 

 intervals independently of the other. 



It is evident, therefore, that the reflex act of winking takes place for 

 each eye upon the same side, undoubtedly in the gray matter of the 

 facial nucleus ; and the two nuclei habitually act in harmony with each 

 other by means of the commissural fibres passing between them. But 

 the mental and emotional influences, which cause the movement of the 

 features in expression or in voluntary acts, are transmitted by decus- 

 sating fibres from the opposite side of the brain. 



This is still further indicated by the different effects caused by peri- 

 pheral and central lesions of the facial nerve. In man, as in animals, if 

 this nerve be divided or destroyed during or after its passage through 

 the aqueduct of Fallopius, all the movements of the facial muscles are 

 paralyzed together. But in cases of facial paralysis depending upon a 

 lesion in the cerebrum itself, that is, above the situation of the nucleus, 

 it is generally observed, according to Yulpian and Hammond, 1 that the 

 loss of movement is not complete; but that, while all the other parts of 

 the face are paralyzed, the patient retains the power of winking on the 

 affected side. This peculiarity is even given as a means of diagnosis 

 between facial paralysis dependent upon injury of the nerve itself and 

 that caused by a lesion in the brain. 



Sensibility of the Facial Nerve. Although this nerve is exclusively 

 motor at its origin, it receives filaments of communication from the fifth 

 pair, which give it a certain degree of sensibility. The most important 

 of these branches, given off from the inferior maxillary division of the 

 fifth nerve, joins the facial soon after its emergence from the stylo- 

 mastoid foramen, and runs forward with its principal branches and rami- 

 fications. The facial nerve, therefore, according to the united testimony 

 of all modern experimenters, if examined upon the side of the face, is 

 found to be sensitive to mechanical irritations, although the degree of 

 its sensibilty is much less than that of the fifth pair. Owing to this 

 communication, the pain, in cases of tic douloureux, sometimes follows 

 the course of the horizontal branches of the facial nerve. The proof, 

 however, that the sensitive fibres of this nerve are derived from its 

 anastomoses and do not orginally form a part of its trunk, is that the 

 sensibility of the facial regions to which it is distributed disappears 

 completely after division of the fifth pair, notwithstanding that the facial 

 nerve itself remains entire. 



Beside the principal communication above mentioned, this nerve con- 

 tracts abundant anastomoses, at the anterior part of the face, with the 

 radiating filaments of the supraorbital, infraorbital, and mental branches 

 of the fifth pair. 



1 Diseases of the Nervous System. New York, 1871, p. 78. 



